Thoracic Anesthesia Flashcards
Describe the hemodynamic changes seen in pulmonary hypertension
- fixed afterload d/t increased pressure in the pulmonary artery
- preload-dependent BUT TOO MUCH RV volume overload shifts the interventricular septum to the LV –> lower systemic CO
- high demand conditions may be detrimental: severe exertion, pregnancy (labor)
*PA pressure = CO (right-side) x PVR + LA pressure
*Cor Pulmonale - RV failure d/t high PAP
*pulmonary capillaries: greatest drop in pressure and increase in resistance
List drugs that are considered pulmonary vasodilators
- calcium channel blockers: nifedipine, diltiazem, amlodipine - block contraction of pulmonary artery smooth muscle
- prostacyclin analog: epoprosterenol
- inhaled NO
- PDE-5 inhibitors: sildenafil
- Nitrates: NTG, sodium nitroprusside
Differentiate nitroglycerin from nitroprusside
Nitroglycerin
- venous > arterial dilation
- decrease preload
- coronary vasodilator: preferred if with concurrent ischemic episodes
- WOF: methemoglobinemia
Sodium Nitroprusside
- equal venous & arterial dilation
- decrease afterload
- reported coronary steal
- WOF: methemoglobinemia, cyanide toxicity
Conduct of anesthesia for pulmonary hypertension
Inducting agent: propofol, etomidate (ketamine - controversial increase in PVR)
Avoid histamine-releasing NMB
Avoid high concentrations of volatile agents, and use of N2O
Avoid excessive hypotension, RV afterload to ensure perfusion
Adequate pain control and normothermia
What should be avoided triggers of increased PVR?
hypoxia
hypercarbia
acidosis
Ventilation strategies for pulmonary hypertension
a) ‘luxury’ oxygenation FiO2 0.6-1.0
b) low TV ~6ml/kg IBW
c) moderate hyperventilation PaCO2 30-35 mmHg
d) avoid metabolic acidosis pH > 7.4
e) PEEP 5-10 cmH2O
*maximize FiO2 first before increasing PEEP to minimize the hemodynamic effect of high PEEP on preload
Vasoactive use in pulmonary hypertension
Vasopressin - choice
Vasopressin, Epinephrine, Dopamine (no/minimal effect on PVR)
Dobutamine, milrinone (lowers PVR): do not use alone because of systemic vasodilation
NE
phenylephrine, ephedrine - AVOIDED
*Maintain systemic pressure above pulmonary pressure to preserve coronary blood flow
Expected ABG finding during an asthma attack
respiratory alkalosis
hypoxemia
hypocarbia
*CO2 retention is a late finding of severe and prolonged airway obstruction i.e. status asthmaticus
Earliest benefit of smoking cessation
12 hours - lower carboxyhemoglobin levels, rightward shift of the hemoglobin dissociation curve
*6-8 weeks - optimal for elective surgery
Anesthetic considerations for asthmatics/COPD (GA/RA)
1) block airway reflexes esp. during airway manipulation
2) relax airway smooth muscles
3) prevent release of biochemical mediators
Propofol or ketamine
Sevoflurane > desflurane > isoflurane (least pungent)
Avoid histamine-releasing NMB e.g. atracurium, mivacurium
LMA over intubation if possible
Neuraxial block: avoid block above T10 - may reduce effective coughing
Ventilation strategies for asthma/COPD
- pressure control over volume control
- increase expiratory time: I/E ratio
- permissive hypoventilation/hypercapnia
- PIP < 50 cmH2O
- Plateau pressure < 30 cmH2O
What is auto-PEEP?
Auto-PEEP or intrinsic PEEP aka breath stacking
- inadequate exhalation –> gas trapping –> increasing intrathoracic pressure –> (a) barotrauma, volutrauma, dyssynchrony
(b) lower VR –> CV collapse
- in mechanically ventilated patients w/ asthma/COPD
Most common cause of intraoperative bronchospasm
Inadequate depth of anesthesia
How to proceed in case of intraoperative wheezing/bronchospasm?
Increase FiO2 while looking for causes
- check PIP, plateau pressure (possible differentials)
- check ETT & circuit
- auscultate chest
- stop surgical stimulation: traction on the mesentery, GIT –> vagal reflex
- LAST: B-agonist 8-10 puffs via ETT
How to differentiate between changes in inspiratory and plateau pressures?
HIGH PIP, N plateau: resistance - kinked ETT/circuit, mucus plug
HIGH PIP & plateau: compliance - pneumonia, pulmonary edema
Describe O2 support in COPD
Titrate to maintain O2sat 88-92%
Giving 100% O2 –> HPV is inhibited –> V/Q mismatching
When to opt for delayed extubation?
Especially for thoracic/upper abdominal incisions:
- PaCO2 > 50 mmHg
- FEV < 1 L
- FVC < 50%
- FEV/FVC < 50%
Agents given to minimize aspiration pneumonitis
a) H2 blockers
b) non-particulate antacid
c) prokinetic
d) PPI
*usually given pre-induction
In case of suspected aspiration:
- head-down position
- 100% O2
- secure airway
- deepen anesthesia
- suction
*no benefit from antibiotics or corticosteroids
Methods to use for lung isolation
a) single lumen tube: advance into the non-operative bronchus
b) double lumen tube: L-sided is preferred for most procedures
c) bronchial blocker: preferred for those already intubated or requiring post-op ventilation
*L-DLT refers to the bronchial tube inserted into the L bronchus
Describe physiology of one-lung ventilation
OPERATIVE LUNG UP
Dependent lung - receives more ventilation & perfusion d/t gravity
Stopping the ventilation –> collapses the lung for surgical access/view
Stopping ventilation to the operative lung –> right-to-left shunt & relative hypoxemia
HPV modulates blood flow to minimize V/Q mismatch
Mech Vent settings during OLV
Small TV ~6ml/kg
PEEP 4-6 cmH2O
Permissive hypercapnia
Avoid long I/E ratio
Pressure control
Why is permissive hypercapnia done?
Promotes HPV –> rightward shift of hemoglobin dissociation curve –> better O2 delivery
What to do to avoid inhibition of HPV?
Treat metabolic/respiratory alkalosis, hypocapnia, hypothermia
Avoid using >1 MAC
Patient develops hypoxemia during OLV
FiO2 1.0
Optimize TV, PIP, and CO
Check DLT/blocker placement
Suction
Add PEEP 5cmH2O to recruit ventilated lung
Add CPAP 5-10cmH2O to decrease shunt in the non-dependent lung
Alert the surgeon - may need to clamp PA to the non-dependent lung
LAST: return to two-lung ventilation
Use of DLT
Confirmation via fiberoptic bronchoscopy (L-DLT: visible R mainstem bronchus, blue bronchial cuff just below the carina in the L mainstem bronchus)
Inflate bronchial cuff + clamp bronchial tube –> collapse bronchial side
Inflate bronchial cuff + clamp tracheal tube –> collapse opposite side
Possible situations where a right-sided DLT is preferred
surgical manipulation on/around the left mainstem bronchus
left pneumonectomy
anatomical variation of the the left mainstem bronchus
